Sunset Birthday Time

Dimanche, 2 mai, 2021 - 9:35 PM

4 minutes read

Every one of your birthdays, the Sun sets at the same time

Since January, we've been under an 8:00 PM curfew in Montréal. On May 3rd, it's being pushed to 9:30 PM.

At the beginning of the 8:00 PM curfew in January, while a bit bizarre that I couldn't leave my house for threat of a fine, the Sun was setting at 4:30 PM. It was dark and cold, so not being allowed out past 8:00 PM didn't seem that unreasonable.

Since the curfew began, I've been writing a tweet each Monday morning saying how much daylight we'll be gaining over the following week, so I've been unusually tapped in to sunset times over the last four months. Sometime in February, with the curfew extended and still set at 8:00 PM, I noticed that an interesting thing would be happening soon: Daylight Saving Time will kick in on March 14, and our sunset time will be one hour later.

On March 13, the Sun set at 5:57 PM. On March 14, 6:59 PM.

But of course, even after the Sun sets, it's still light out (this is called Twilight – here's a really interesting read on the Different Types of Twilight). By the end of March, it would be light outside and people would be required to be inside.

What would the provincial government do?

When late March rolled around, the curfew was briefly pushed back to 9:30 PM, but was quickly reverted back to 8:00 PM as cases looked to be on the rise.

Sunset from Parc La Fontaine

Tracking 8:00 PM

Doing my weekly tweets about sunset times, I noticed that the Sun would set here in Montréal on the last day of April at 8:00 PM. You can check yourself. But does this happen every year?

It varies slightly each year, but is basically 8:00 PM each go-around:

So here's an easy shorthand: "Sunsets start at 8:00 on the First Day of May in Montréal."

I invite a poet or lyricist to make that more catchy.

At first this seemed really odd: why does the Sun set at the same time on each date every year? My gut tells me that there would be some variation, no? But then thinking for a moment, we've based our Gregorian calendar around the Sun. Through careful observation, ancients found that the Sun returned to the same place in the sky every 365 days.

I can't go into detail in this brief blog post, but in short: our calendar is a human construct based on nature. What we observe on those dates is a reflection of what we see happening in nature. In this case, the Sun setting.

Different Cities

A quick note: the Sun sets at same time on the same date each year in the same city. If I check the Sunset time for April 30th in Toronto, it will be different times, but the effect is the same. The Sun sets at the same time for that location:

Sunset Birthday Time

Suddenly: a light switch turns on in Trevor's brain! If the Sun sets at the same time on the same date each year, it must set at the same time on my birthday! And indeed, it does.

My birthday is July 15th. In Montréal, my Sunset Birthday Time is 8:39 PM. See for yourself.

This will always be true: the Sun will always set at 8:39 PM on my birthday in Montréal.

And in my hometown, Drayton Valley my Sunset Birthday Time is 9:58 PM. Check it.

Check Your Own

Go to TimeAndDate.com and search for your location (or maybe where you were born). Search for your birthday and find your Birthday Sunset Time. You could even find your Birthday Sunrise Time!

Because our calendar is based on the Sun, those times will remain constant for the location you search for. Fun!

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